1. Field of the Invention
The present invention generally relates to an input buffer circuit which is provided at the input section of a digital circuit, and, in particular, to such an input buffer circuit comprised of MOSFETs.
2. Description of the Prior Art
In digital circuits such as programmable logic arrays (PLAs), programmable array logics (PALs) and programmable read only memories (PROMs), in addition to a two-level signal having low and high states, it is often required to use a signal of higher level, for example, for programming. In a circuit requiring an input signal of three or more levels, the number of input pins, when manufactured as a semiconductor device, is required to be increased corresponding to the number of levels of input signal. For this reason, the resulting device tends to become larger in size and higher in cost.